1. Field of the Invention
This invention relates to a motor assembly, more particularly to a brushless electric motor assembly having an axial tube for reliably positioning an antifriction bearing.
2. Description of the Related Art
Referring to FIG. 1, a motor structure disclosed in U.S. Pat. No. 6,882,074 B2 includes a stator 14 and a circuit board 13 which are engaged together and which are mounted to a hollow tube of a casing 11, and an axial tube 12 mounted into the hollow tube of the casing 11 from a bottom end of the hollow tube and in splined engagement therewith such that hook portions 122 of a plurality of resilient arms 121 are brought into engagement with the stator 14. A positioning ring 10, a supporting member 17, and an abrasion-resisting plate 20 are mounted into the axial tube 12. A sleeve 15 having a bearing 16 mounted therein is inserted into and is tightly engaged with the axial tube 12. A shaft 18 of a rotor 19 extends through the bearing 16 and the positioning ring 10. Since the axial tube 12 and the sleeve 15 exert forces on each other, the sleeve 15 is tightly engaged with the bearing 16, and the resilient arms 121 are securely engaged with the stator 14.
However, due to the arrangement of the open-ended sleeve 15, lubricating oil between the bearing 16 and the shaft 18 may leak through the bottom of the sleeve 15 by virtue of gravity, thereby adversely affecting running of the shaft 19 and resulting in generation of noise. Moreover, since the axial tube 12 and the sleeve 15 are preferably made from a plastic material in order to facilitate fitting engagement, the structural strength thereof is relatively low, so that deformation may occur during assembly.